Mobile communication control method, cellular system, mobile station, base station, and base station control apparatus

ABSTRACT

To decrease the number of base stations transmitting when a mobile station is connected to a plurality of base stations during handover and to let a base station having the best reception quality perform transmission so as to decrease interference in downlink and increase the link capacity. A mobile station periodically measures a pilot signal transmitted from a base station in a reception monitor  406  and estimates its own movement speed at predetermined intervals based upon the reception electric field strength of the pilot signal in a speed estimate device  407  in soft handover state. A time length for measuring the pilot signal transmitted from the base station corresponding to the movement speed and an inner threshold value for deciding transmission base stations during handover are altered in a control section  408 . In this case, when the movement speed is slow, the pilot signal measurement time length is set short, and the inner threshold value is set small, and when the movement speed is fast, the pilot signal measurement time length is set long, and the inner threshold value is set large.

TECHNICAL FIELD

The present invention relates to a mobile communication control methodand a cellular system in which the number of base stations transmittingduring handover is decreased and which are suitably employed in a casewhere a probability that an optimum base station for a mobile stationtransmits is increased and a mobile station and a base stationcontroller which are employed therefor.

BACKGROUND ART

In a cellular system employing direct sequence code divisional multiaccess, since the same frequency bands are employed in a plurality ofchannels, other channels' radio signals become interference, and thereception quality of a desired wave deteriorates when interferenceincrease, thereby causing disconnection of a link or the like.Therefore, the number of links through which talking at the same time ispossible while a constant standard of speech quality is maintained, thatis, a link capacity, depends on the amount of the interference.

Thus, in a cellular system employing the direct sequence code divisionalmulti access, when transmission from a base station to a plurality ofmobile stations is implemented, the transmission power value of the basestation is controlled in order that a downlink signal that each mobilestation generally receives is at a required minimum reception level.That is, a closed loop control is implemented wherein while each mobilestation periodically measures the reception quality of a signal that thebase station transmits, a signal instructing the base station todecrease the transmission electric power is transmitted when themeasured reception quality exceeds a predetermined target value, and asignal instructing the base station to increase the transmissionelectric power is transmitted when the quality is less than thepredetermined target value. Typically, in this control, a high speedclosed loop type control for each slot is performed so that thereception level in a mobile station becomes a minimum reception levelcapable of talking.

In general, in handover of a cellular system employing the directsequence code divisional multi access, a technique called soft handoveris employed. This technique is one in which when a mobile stationreaches to a cell boundary area of a base station with which the mobilestation communicates so that the reception level of downlink decreasesdue to a propagation loss or the like, a link is set up also with a basestation adjacent to the base station to implement simultaneousconnections. Thus, the mobile station periodically measures pilotsignals that each base station transmits at a predetermined electricpower, and when a base station exists in which the difference betweenthe reception level from a presently communicating base station and thatthereof becomes within a predetermined threshold value, base stationsare chosen so that the number of the base stations is within apredetermined maximum number in the order of good quality to implementsimultaneous connections.

In a mobile station during the soft handover, the same down informationis received from a plurality of base stations to implement a diversitysynthesis. In a vicinity of a cell boundary, since the distance from abase station is long, the reception quality deteriorates. Although linkquality tends to deteriorate due to interference from another cell, by adiversity effect caused by connection with such plurality of basestations, deterioration in downlink quality can be prevented.

However, since a plurality of links are employed for one mobile stationin the soft handover, interference in downlink increases compared to acellular system in which the soft handover is not employed, causing aproblem that increase in the link capacity cannot be achieved.

As a technique for solving this problem, Japanese Patent Publication No.H11(1999)-69416 discloses a transmission electric power controltechnique of a base station selection type in which the downlinkcapacity is increased by specifying transmission base stations actuallytransmitting among a base station group during the soft handover.

In this transmission electric power control technique of the basestation selection type, a base station group and links are set upwherein the differences in the reception qualities are within athreshold value, and further transmission base stations to actuallytransmit are selected from among the base station group with which linksare set up. The transmission base station is supposed to be one in whichthe difference in the reception qualities is within an inner thresholdvalue which is smaller than the threshold value of the time of settinglinks up, and the base station other than the transmission base stationwith which links are set up switches its transmission electric power toa predetermined minimum transmission power value. Thus, it becomespossible to reduce interference of downlink while maintaining anadvantage in smooth handover switching in the conventional softhandover, and therefore the link capacity can be increased.

However, since there is a delay time, for transmitting a measured resultto the base station, between time of measuring the reception quality andtime of actually transmitting, and since the reception level is changingdue to fading or the like, the reception level changes during the delaytime, and a drift occurs between the measured result and the receptionquality of the time of actual transmission.

Accordingly, even when a transmission base station is decided in theorder of good quality at the time of measuring the reception quality, acase where a base station having a good quality is not included in thetransmission base stations at the time of actual transmission may occur.In this case, not the best base station but a base station having agreater propagation loss has to transmit. Typically, since the receptionquality at a mobile station is controlled so as to satisfy a desiredstandard by a transmission electric power control of a high speed closedloop type, there is a problem that the transmission electric power of abase station is high, interference electric power for other mobilestations increases, and the link capacity decreases.

Accordingly, it is an object of the present invention to decrease thenumber of transmission base stations and increase the downlink capacitywhile enhancing the possibility that the best base station is included.

DISCLOSURE OF INVENTION

In order to achieve the above described object, a mobile communicationcontrol method according to the present invention is a mobilecommunication control method in a cellular system comprised of aplurality of base stations, a mobile station setting up links with thebase stations, and a base station controller connected to the basestations, wherein a pilot signal is transmitted from the base stationsat a predetermined electric power, a reception quality of each pilotsignal transmitted from the plural base stations is periodicallymeasured, plural base stations with which links are set up are decidedcorresponding to the measurement result, one or more transmission basestations are decided from among the plural base stations with which thelinks are set up to inform the plural base stations with which the linksare set up, each base station controls transmission to the mobilestation corresponding to the information, and the decision is made whenthe transmission base station is decided so that the number oftransmission base stations is made small and the probability that thebest base station in the reception quality of the pilot signal in themobile station is included in the transmission base stations is madehigh based upon a predetermined condition, wherein a measurement timelength of the reception quality of the pilot signal in the mobilestation is altered for each mobile station.

A cellular system according to the present invention is a cellularsystem composed of a plurality of base stations, a mobile stationsetting up links with the base stations, and a base station controllerconnected to the base stations, wherein a pilot signal is transmittedfrom the base stations at a predetermined electric power, the basestation periodically measures a reception quality of each pilot signaltransmitted from the plural base stations, the plural base stations withwhich links are set up are informed of one or more transmission basestations from among the plural base stations with which links are setup, each base station controls transmission to the mobile stationcorresponding to the information, and when the transmission basestations are decided, the decision is made based upon a predeterminedcondition, whereby the number of transmission base stations is madesmall and the probability that the best base station in the receptionquality of the pilot signal in the mobile station is included in thetransmission base stations is made high, wherein a measurement timelength of the reception quality of the pilot signal in the mobilestation is altered for each mobile station.

A mobile station according to the present invention comprises ameasurement means for periodically measuring a reception quality of apilot signal transmitted from plural base stations, a decision informingmeans for deciding one or more transmission base stations from amongplural base stations with which links are set up corresponding to themeasurement result and for informing the plural base stations with whichthe links are set up of the decision result, said decision being madebased upon a predetermined condition so that the number of transmissionbase stations is made small and the probability that the best basestation in the reception quality of the pilot signal in the mobilestation is included in the transmission base stations is made high, anda alteration means for altering a measurement time length of thereception quality of the pilot signal by the measurement means basedupon a movement speed detected in the base station or the mobilestation.

A base station controller according to the present invention comprises asetting informing means for setting a measurement time length forperiodically measuring a reception quality of a pilot signal that amobile station receives from a base station for each mobile station toinform the mobile station of the set measurement time length.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is characteristic views showing examples of pilot signalreception levels in a mobile station in a case where the movement speedof the mobile station is slow for in principle explaining embodiments ofthe present invention.

FIG. 2 is characteristic views showing examples of pilot signalreception levels in a mobile station in a case where the movement speedof the mobile station is fast for in principle explaining embodiments ofthe present invention.

FIG. 3 is a block diagram of a cellular system according to a firstembodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of a mobile stationaccording to the first embodiment of the present invention.

FIG. 5 is a block diagram showing the configuration of a base stationaccording to the first embodiment of the present invention.

FIG. 6 is a block diagram showing the configuration of a base stationcontroller according to the first embodiment of the present invention.

FIG. 7 is a flow chart showing operations of the mobile stationaccording to the first embodiment of the present invention.

FIG. 8 is a block diagram showing the configuration of a mobile stationaccording to a second embodiment of the present invention.

FIG. 9 is a block diagram showing the configuration of a base stationcontroller according to the second embodiment of the present invention.

FIG. 10 is a flow chart showing operations of the base stationcontroller according to the second embodiment of the present invention.

FIG. 11 is a block diagram showing the configuration of a mobile stationaccording to a third embodiment of the present invention.

FIG. 12 is a block diagram showing the configuration of a base stationaccording to the third embodiment of the present invention.

FIG. 13 is a block diagram showing the configuration of a mobile stationaccording to a fourth embodiment of the present invention.

FIG. 14 is a block diagram showing the configuration of a base stationaccording to the fourth embodiment of the present invention.

FIG. 15 is a block diagram showing the configuration of a base stationaccording to a fifth embodiment of the present invention.

FIG. 16 is a block diagram showing the configuration of a base stationaccording to the sixth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are explained below, referring todrawings.

In the present embodiments, one or a plurality of base station transmitsa pilot signal at a predetermined electric power, and the receptionquality of each pilot signal transmitted from the one or plurality ofbase station is periodically measured in one or a plurality of mobilestation. One or a plurality of base station with which a link is set upis decided in accordance with a measured result, and one or a pluralityof transmission base station is selected from the one or plurality ofbase station decided.

A characteristic of the present invention is that a predeterminedcondition deciding a transmission base station such as, for example, apropagation environment or a change in a propagation environment, ischanged for each mobile station. Further, a characteristic of thepresent invention is that transmission base stations are decided so thatthe number of transmission base stations is as small as possible, andthe probability that a base station whose reception quality of a pilotsignal in a mobile station is the best is included in transmission basestations becomes high, based upon a predetermined condition.

First, prior to the explanation in detail of an embodiment of thepresent invention, the present embodiment is explained in principle.Employed is an example of a case where the movement speed of a mobilestation is employed as a specific example of a propagation environmentor a change in a propagation environment that is an example of apredetermined condition.

When it is supposed that a mean value or the like of the receptionlevels during a measurement time is employed as a result of thereception quality measurement of the pilot signal in a mobile station,the drift between the reception qualities of the measurement time andthe transmission time largely depends upon a fading pitch and ameasurement time length changing in accordance with the movement speed.

This is explained in detail referring to FIG. 1 and FIG. 2.

FIG. 1 shows an example of reception levels in a mobile station fromhandover base stations BS1, BS2 of a case where the speed is slow, thatis, a case where the fading pitch is small.

In the drawing, shown are a measurement time 1 of a case where themeasurement time is short, a measurement time 2 of a case where themeasurement time is long, a delay time for deciding a transmission basestation from a measurement result of the reception quality and forinforming a base station in which a link has been set up, and atransmission time during which transmission is actually implemented fromthe transmission base station. An electric power level S in the drawingis a standard value for comparing BS1 with BS2, and the sama electricpower level value is supposed at BS1 and BS2. In the case of this FIG.1, in the reception level at a time of actual transmission, BS1 ishigher than BS2.

When it is supposed that the value of the reception quality by themeasurement is the mean value of the reception levels during themeasurement time, in a case where measurements are performed in themeasurement time 1, the measurement result of BS1 is reception level Aand that of BS2 reception level B. In this case, a base station havingthe best reception quality is decided as BS1.

However, when the measurements are performed in the measurement time 2,the measurement result of BS1 is reception level C and that of BS2reception level D, and D is greater than C in this case. Accordingly,the base station having the best reception quality is decided as BS2.Since transmission base stations are selected in the order of goodreception quality, the probability that the base station BS1 best at thetransmission time is selected as a transmission base station becomes lowin this case.

FIG. 2 shows a case where the speed of a mobile station is fast, thereception quality at the actual transmission time shows a case where BS1is better than BS2 similarly to FIG. 1, and measurement times, a delaytime, a transmission time, and a reception level to be a standard arealso shown similarly to FIG. 1.

In the case shown in FIG. 2, when measurements are performed in themeasurement time 2, the measurement result of BS1 is reception level Gand that of BS2 reception level H, and G is greater than H as obviousfrom the drawing. Accordingly, the base station BS1 having the bestreception quality at the transmission time is decided as one having thebest reception quality.

However, when measurements are performed in the measurement time 1, themeasurement mean of BS1 is reception level E and that of BS2 receptionlevel F, and F is greater than E as obvious from the drawing.Accordingly, a base station having the best reception quality is decidedas BS2, and the probability that the base station BS1 best at thetransmission time is included in transmission base stations becomes low.

As described above, since the fading pitch is small when the movementspeed is slow, when the reception level fluctuation is small, themeasurement time is short, and a mean value only for a time as close aspossible to the transmission time is employed, the probability that thebest base station is included in transmission base stations becomeshigh. In a case where the movement speed is fast, since the fading pitchis large and the reception level fluctuation is large, when themeasurement time is long, and an averaged value of fading is employed,the probability that the best base station is included in transmissionbase stations becomes high.

However, since the measurement time is constant regardless of speed inthe transmission electric power control technique of the conventionalbase station selection type, there is a problem that the probabilitythat the best base station is included in transmission base stationsbecomes low.

The relationship between the size of the inner threshold value to be thestandard of the time of actually deciding transmission base stations andthe movement speed influences the probability that the best transmissionbase station at the time of transmission is included.

Since a base station within the inner threshold value becomes atransmission base station, the greater the inner threshold value, thehigher the probability that the number of transmission base stationsbecomes large is. Therefore, the probability that the best base stationis included in transmission base stations becomes high. However, sincethe number of links for one mobile station increases when the number oftransmission base stations increases, interference of links increases asa whole, and thus the link capacity decreases.

When the speed of a mobile station is slow and the fading pitch issmall, since a reception quality fluctuation during the delay time fromthe measurement of the reception quality to the time a transmission basestation actually transmits is small, the difference between the order ofgood base stations in the reception quality determined from themeasurement result and the order of good base stations actually at thetime of transmission is small. Accordingly, when the movement speed isslow, even when the inner threshold value is small, the probability thata base station having the best reception quality becomes a transmissionbase station is large, and the larger the inner threshold value, themore interference increases as a whole since a base station having apoor reception condition comes to be included in transmission basestations.

When the speed of a mobile station is fast and the fading pitch islarge, since the reception quality fluctuation during the delay time islarge, the difference between the orders of reception qualities of thetime of the reception quality measurement and of the time of actualtransmission becomes large. Accordingly, when the inner threshold valueis small, the probability that a base station having the best receptionquality at the time of transmission is not included in transmission basestations becomes high.

As described above, it can be understood that it is better that theinner threshold value is small when the movement speed is slow, and thatthe faster the movement speed the larger the inner threshold value is.

Although the value of an optimum inner threshold value differs dependingupon the speed of a mobile station, an inner threshold value is constantin the transmission electric power control technique of the conventionalbase station selection type, and deciding transmission base stationsunder optimum conditions in accordance with the speed is not performed.Thus, the best base station is not included in transmission basestations, or unnecessary transmission base stations increase, and thusthere is a problem that interference of links increases and the linkcapacity decreases.

Therefore, in the present embodiment, by changing the reception qualitymeasurement time length and the inner threshold value of the pilotsignal in accordance with the speed of each mobile station, the numberof transmission base stations is minimized, the possibility of that thebest base station is included is made higher, and downlink capacity isincreased. At that time, the faster the movement speed of a mobilestation, the longer the measurement time length is taken, and the fasterthe movement speed of a mobile station, the greater the inner thresholdvalue is taken.

FIG. 3 is a block diagram of a cellular system to which the presentinvention is applied.

In FIG. 3, base stations 301 to 303 transmit to mobile stations 331, 332within regions of respective cells 311 to 313. The respective basestations are connected to a base station controller (BSC) 321. Each ofthe base stations transmits a predetermined electric power value ofpilot signal whose subject is all mobile stations in its cell and anindividual signal for each mobile station, and the transmission electricpower of the individual signal for each mobile station is controlled bya high speed closed loop type control.

A mobile station periodically measures the reception qualities of thepilot signals transmitted from respective base stations to decide basestations with which links are set up. Links are set up with a basestation having the best reception quality and a base station in whichthe difference between the reception quality thereof and the receptionquality of said base station having the best reception quality is withina predetermined threshold value.

With respect to the base station 331 located in a vicinity of the centerof the cell 311, since the reception quality from the base station 301is the best, and since the reception qualities of signals from othercells are not within a predetermined threshold value, the base station331 sets up a link only with the base station 301 to communicate.

Since the mobile station 332 is located in a vicinity of the boundary ofthe cell 311, the reception quality from the base station 301deteriorates by the propagation loss, and the reception qualities of thesignals from the base stations 302, 303 are in a state where thedifferences between the reception quality of the base station 301 andthe reception qualities of the base stations 302, 303 are within apredetermined threshold value. Accordingly, at this time the mobilestation 332 sets up links with the three base stations 301 to 303.Further, an inner threshold value smaller than said threshold value isset, and a base station whose reception quality is within an innerthreshold value is selected as a transmission base station from amongthe base stations 301 to 303 with which said links are set up toactually transmit. The base stations with which links are set up andwhich are not transmission base stations switch the transmissionelectric power to a predetermined minimum value.

When the reception qualities from the base stations 301, 302 are withinthe inner threshold value, the base stations 301, 302 are selected astransmission base stations, and individual signals are transmitted at anelectric power value controlled by the general high speed closed loopcontrol. Since the reception quality of the base station 303 is notwithin the inner threshold value and is a non-transmission base station,the individual signal is transmitted at a minimum transmission powervalue.

FIG. 4, FIG. 5, and FIG. 6 show configurations of a mobile station, abase station, and a base station controller according to a firstembodiment of the present invention.

In FIG. 4, the mobile station is comprised of a reception antenna 401receiving a radio signal transmitted from one or a plurality of basestations, a transmission/reception shared device (DUP) 402, a radioreception section (Rx) 403 converting a radio signal into a receptionbase band signal, a reception quality monitor 406 receiving pilotsignals of a plurality of base stations and measuring their receptionqualities, a speed estimate device 407 estimating its own station speedfrom the pilot signals received, a control section 408 controlling inaccordance with the estimated speed, a transmission base stationdesignating section 409 deciding and designating transmission basestations through the reception qualities of the pilot signals, amultiplexer (MUX) 410 multiplexing a base station designating signal andinput data and generating an up-transmission signal, a spread circuit411 spreading the up-transmission signal and outputting a transmissionbase signal, a radio transmission section (Tx) 412 converting thetransmission base signal into a radio signal to transmit it, a RAKEreceiver 404 synthesizing base signals from a plurality of transmissionbase stations, and a demultiplexer (DMUX) 405.

The speed estimate device 407 detects a fading pitch from a receptionelectric field strength of a received signal and from this detectionresult estimates its own station movement speed.

The control section 408 is comprised of a pilot signal measurement timelength specifying section 413 and an inner threshold value specifyingsection 414, and each of these specifies a value corresponding to theestimated speed.

The reception quality monitor 406 measures the reception levels of thepilot signals transmitted from base stations only for a time lengthspecified through the pilot signal measurement time length specifyingsection 413 and informs the transmission base station designatingsection 409 of its results.

The transmission base station designating section 409 designates a basestation group whose reception quality differences are within thethreshold value as base stations with which links are set up through themeasurement results of the reception levels and selects a transmissionbase station actually transmitting from among the base station groupwith which links are set up. The transmission base station is supposedto be a base station whose reception quality difference is within theinner threshold value which is smaller than the threshold value of thetime when a link is set up. Specifically, a base station whose receptionquality is the best and a base station in which the difference betweenthe reception quality of the base station and the reception quality ofitself is within a threshold value specified by the inner thresholdvalue specifying section are decided as transmission base stations sothat a signal designating transmission base stations is generated. Thistransmission base station designating signal is transmitted to one or aplurality of base stations with which links are set up.

In FIG. 5, a base station is comprised of a reception antenna 501receiving a radio signal transmitted from a mobile station, atransmission/reception shared device (DUP) 502, a radio receptionsection (Rx) 503 converting a radio signal into a reception base bandsignal, a RAKE receiver 504 synthesizing a base signal, a demultiplexer(DMUX) 505, an output terminal 506 transmitting a signal separated by ademultiplexer to the base station controller, an input terminal 507inputting a control signal from the base station controller, atransmission electric power control section 508 controlling thetransmission electric power of its own station in accordance with thetransmission base station designating signal separated by thedemultiplexer, a multiplexer (MUX) 509, a spread circuit 510 outputtingthe transmission base signal, and a radio transmission section (Tx) 511converting the transmission base signal into a radio signal to transmit.

The transmission electric power control section 508 transmits at atransmission power value according to a general high speed closed looptransmission electric power control when its own station is atransmission base station in accordance with the transmission basestation designating signal transmitted from a mobile station andswitches the transmission electric power to a predetermined minimumtransmission power value when its own station is not a transmission basestation.

In FIG. 6, the base station controller is comprised of an input terminal601 receiving a signal transmitted from the base station, a receptionprocessing section 602, a control section 603 performing variouscontrols regarding transmission and reception of a base station, atransmission processing section 604, and an output terminal 605transmitting a signal to each base station.

FIG. 7 is a flow chart showing operations of the mobile stationaccording to the first embodiment of the present invention. Changes ofthe pilot signal measurement time length and the inner threshold valueperformed for each predetermined time during operations of change of atransmission base station that the mobile station periodically performsis explained below.

First, when it is at change timing of the pilot signal measurement timelength and the inner threshold value performed for each predeterminedtime (step 701, YES), the fading pitch is measured through a pilotsignal reception level from a measured base station and estimates amovement speed V of its own station (step 702).

When this estimated speed V is greater than a speed Vth1 (step 703,YES), a pilot signal measurement time length T is set as a predeterminedvalue T1 (step 704), and when the estimated speed V is smaller than thespeed Vth1 (step 703, NO), the pilot signal measurement length T isaltered to T2 (step 705). In this case, T1 is greater than T2. When theestimated speed V is greater than a speed Vth2 (step 706, YES), an innerthreshold value E is set as a predetermined value E1 (step 707), andwhen the estimated speed V is smaller than the speed Vth2 (step 706,NO), the inner threshold value E is altered to E2 (step 708). In thiscase, E1 is greater than E2.

If it is not at the change timing of the measurement time length and theinner threshold value (step 701, NO), the measurement time length andthe inner threshold value are not altered.

The reception quality of the pilot signal is measured only for themeasurement time length T (step 709).

Among a base station having the best reception quality in the measuredbase station group and base stations in which the differences in thereception qualities of the base station having the best receptionquality and of said base stations are within a set inner threshold valueE, base stations are decided as transmission base stations up to apredetermined maximum number of transmission base stations in the orderof good reception qualities, and a signal designating transmission basestations is transmitted (step 710).

Such change of transmission base stations is periodically performedwhile the mobile station is performing the handover.

Next, entire operation of the present embodiment is explained.

Operations forming a basis of the present embodiment are two, that is, achange in the measurement time length of the pilot signal correspondingto the speed of a mobile station and a change in the inner thresholdvalue.

The optimum pilot measurement time length differs according to themovement speed of a mobile station. When the movement speed is slow, thereception level fluctuation during the delay time until transmission isactually performed is small.

Thus, in the present embodiment, when the movement speed is slow, thepilot measurement time length is set short, and a mean value only for atime period close to the transmission time is employed. Therefore, thedifference in the reception qualities of transmission times can be madesmall, and the probability that the best base station is included as atransmission base station can be made higher.

When the movement speed is fast, the reception level fluctuation duringthe delay time until transmission is actually performed is large, and ameasurement mean in a short time period becomes a mean only for a partof a moment value, whereby the difference between said mean and anaverage reception level in the transmission time period becomes large.

Thus, in the present embodiment, when the movement speed is fast, thepilot measurement time length is made longer, and a value obtained byaveraging fading fluctuation is employed, whereby the probability that abase station that is best at the transmission time is included intransmission base stations can be made higher.

The greater the inner threshold value, the higher the probability thatthe number of transmission base stations becomes large, and thus theprobability that the best base station is included in transmission basestations becomes high. However, when the number of transmission basestations increases, since the number of transmission signals for onemobile station increases, interference as a whole increases.

Thus, in the present embodiment, when the speed is slow and thereception level fluctuation is small, that is, when the differencebetween the measured result and an actual one in the transmission timeis not easily manifested, by specifying a small inner threshold value,unnecessary transmission base stations can be decreased withoutdeteriorating the probability that a base station having the bestreception quality is included in transmission base stations.

By specifying a greater inner threshold value when the speed is fast,even when the reception level fluctuation is large and the differencebetween the measured result and an actual one in the transmission timeis easily manifested, the probability that a base station having thebest reception quality is included in transmission base stations can bemade higher.

Thus, in the present embodiment, since transmission base stations aredecided by conditions corresponding to each movement speed so that thenumber of transmission base stations is decreased and the probabilitythat a base station having the best reception quality in thetransmission time is included in transmission base stations is madehigher, interference of links is reduced, and link capacity can beincreased.

Next, a second embodiment of the present invention is explained.

FIG. 8 and FIG. 9 are diagrams showing configurations of a mobilestation and a base station controller according to the presentembodiment, the same reference numerals are designated for thecorresponding parts to those in FIG. 4 and FIG. 6, and overlappingexplanation thereof is omitted.

The base station according to the present embodiment is the same as thatof the first embodiment of FIG. 4. The cellular system to which thepresent embodiment is applied is the same as that of FIG. 3.

In FIG. 8, the mobile station according to the present embodiment is notprovided with the control section 408 with which the mobile station ofFIG. 4 is provided. In compensation therefor, a signal representing thespeed of the mobile station estimated by the speed estimate device 407at predetermined time intervals is outputted to the multiplexer (MUX)410, is multiplexed onto the transmission signal, and is transmitted tothe base station.

Signals specifying the pilot signal measurement time length and theinner threshold value which are multiplexed onto the transmission signalfrom the transmission base station are separated in the demultiplexer(DMUX) 405 so as to inform the reception quality monitor 406 of thepilot signal measurement time length and the transmission base stationdesignating section 409 of the inner threshold value. Operations ofother components of FIG. 8 are performed similarly to those of themobile station of FIG. 4.

The base station controller according to the present embodiment isprovided with a pilot signal measurement time length specifying section606 and an inner threshold value specifying section 607 with which thebase station controller of FIG. 6 is not provided as shown in FIG. 9.

The base station controller separates a signal representing the movementspeed of the mobile station which is multiplexed at predetermined timeintervals onto the signal transmitted from the mobile station andinforms the pilot signal measurement time length specifying section 606and the inner threshold value specifying section 607 of its estimatedspeed. The pilot signal measurement time length specifying section 606and the inner threshold value specifying section 607 decide a receptionquality measurement time length of a pilot signal and an inner thresholdvalue corresponding to the estimated speed, multiplex signals specifyingthe respective length and value onto the transmission signal, and informthe mobile station via the transmission base station from thetransmission processing section 604. Operations of other components ofFIG. 9 are performed similarly to those of the base station controllerof FIG. 6.

FIG. 10 is a flow chart showing operations of the base stationcontroller of the present embodiment. Control for specifying changes ofthe pilot signal measurement time length and the inner threshold valueperformed at predetermined time intervals is explained below.

First, the base station controller receives the transmission signal fromthe mobile station via the transmission base station (step 1001). Whenit is at change timing of the pilot signal measurement time length andthe inner threshold value (step 1002, YES), a signal informing of themovement speed V estimated in the mobile station is multiplexed onto thetransmission signal from the mobile station, and the base stationcontroller separates the signal (step 1003).

When the estimated speed V informed is greater than a predeterminedvalue Vth1 (step 104, YES), a measurement time length T of the pilotsignal is specified as T1 (step 1005), and when the estimated speed V issmaller than the speed Vth1 (step 104, NO), a signal specifying thepilot signal measurement length T as T2 (step 1006) is transmitted tothe mobile station via the transmission base station (step 1007). Here,T1 is greater than T2.

When the estimated speed V is greater than a predetermined value Vth2(step 1008, YES), the inner threshold value is specified as E1 (step1009), and when the estimated speed V is smaller than that (step 1008,NO), a signal specifying the inner threshold value as E2 (step 1010) istransmitted to the mobile station via the transmission base station(step 1011). Here, E1 is greater than E2.

If it is not at the change timing of the pilot signal measurement timelength and the inner threshold value (step 1002, NO), the pilot signalmeasurement time length and the inner threshold value are not altered.

The base station controller periodically performs the above describedoperations while the mobile station is performing the soft handover.

As clear from the above, the difference between the first embodiment andthe second embodiment is that although in the case of the firstembodiment, the pilot signal measurement time length and the innerthreshold value are decided in the mobile station side corresponding tothe movement speed of its own station estimated in the mobile station,in the case of the second embodiment, the mobile station multiplexes thesignal representing the estimated movement speed onto the transmissionsignal and informs the base station controller via the base station ofit, and the measurement time length of the pilot signal and the innerthreshold value are decided corresponding to the informed estimatedspeed in the base station controller side and the mobile station isinformed of them.

The operations of the second embodiment are substantially the same asthose of the first embodiment. When the speed is slow and the receptionlevel fluctuation is small, a short pilot signal measurement time lengthis specified, and a mean value only for a time as close as possible tothe actual transmission time is employed. When the speed is fast and thereception level fluctuation is large, a long pilot signal measurementtime length is specified, and an averaged value of fading fluctuation isemployed. Thus, the difference in the reception levels of the receptiontime and of the transmission time can be made smaller, and therefore theprobability that the base station having the best reception quality isincluded in transmission base stations can be made higher.

A small inner threshold value is specified when the difference betweenthe reception result and an actual one in the transmission time is smalldue to a slow speed and a small reception level fluctuation, and a largeinner threshold value is specified when the difference between thereception result and an actual one in the transmission time is large dueto a fast speed and a large reception level fluctuation. Thus,unnecessary transmission base stations can be decreased while theprobability that a base station having the best reception level isincluded in transmission base stations is made higher.

Next, a third embodiment is explained. Although the pilot signalmeasurement time length and the inner threshold value are decidedcorresponding to the movement speed of the mobile station itselfestimated in the mobile station in the cases of the first and secondembodiments, in the third embodiment, the movement speed of the mobilestation is estimated in the base station. Thus, the base station isprovided with a speed estimate device, and the movement speed of themobile station is estimated from a change or the like of a transmissionelectric power control signal periodically transmitted to the basestation with which a link is set up from the mobile station.

When the movement speed of the mobile station is estimated in the basestation, the base station informs the mobile station in which themovement speed is estimated of an estimated result. In the mobilestation, similarly to the first embodiment, the measurement time lengthof the pilot signal and the inner threshold value may be decidedemploying the movement speed estimated in this base station.

FIG. 11 and FIG. 12 show configurations of the mobile station and thebase station according to the third embodiment of the present invention.The base station controller may have a configuration similar to that ofFIG. 6 of the first embodiment.

In FIG. 11, the mobile station according to the present embodiment isnot provided with the speed estimate device 407 with which the mobilestation is provided in FIG. 4. In compensation therefor, a signalrepresenting the speed of the mobile station multiplexed onto thetransmission signal from a transmission base station is separated in thedemultiplexer (DMUX) 405 and is inputted to the pilot signal measurementtime specifying section 413 and the inner threshold value specifyingsection 414 of the control section 408.

Since operations of the control section 408 and operations of othercomponents are similar to those of the first embodiment, explanationthereof is omitted.

In operations of the mobile station in the present embodiment, a signalrepresenting the speed of the mobile station from the base station maybe received at step 702 of FIG. 7 that is a flow chart showingoperations of the first embodiment, and the pilot signal measurementtime length and the inner threshold value may be decided at steps 703,706 based upon that speed V In FIG. 12, the base station according tothe present embodiment is further provided with a speed estimate device517 in the base station shown in FIG. 5. The speed estimate device 517inputs the transmission electric power control signal multiplexed ontothe transmission signal from the mobile station separated in thedemultiplexer (DMUX) 505 and estimates the movement speed of the mobilestation based upon the change in the transmission electric power controlsignal. The signal representing the speed of the mobile stationestimated by the speed estimate device 517 is outputted to themultiplexer (MUX) 509, is multiplexed onto the transmission signal, andis transmitted to the corresponding mobile station.

Since other operations in the base station are similar to those of thefirst embodiment, they are omitted.

Next, a forth embodiment is explained. In the third embodiment, themovement speed of the mobile station is estimated in the base station,and the corresponding mobile station is informed of the estimatedmovement speed. In the forth embodiment, the base station controller isinformed of the movement speed of the mobile station estimated in themobile station, the pilot signal measurement time length and the innerthreshold value are decided in the base station controller similarly tothe second embodiment, and the corresponding mobile station is informedof them via the base station. The mobile station alters the pilot signalmeasurement time length and the inner threshold value based upon theinformation from the base station controller.

FIG. 13 and FIG. 14 are diagrams showing configurations of a mobilestation and a base station according to the fourth embodiment of thepresent invention, the same reference numerals are designated for thecorresponding parts to those in FIG. 8 and FIG. 5, and overlappingexplanation thereof is omitted. The base station controller according tothe present embodiment is the same as that of the second embodiment ofFIG. 9. The cellular system to which the present embodiment is appliedis the same as that of FIG. 3.

In FIG. 13, the mobile station according to the present embodiment isnot provided with the speed estimate device 407 with which the mobilestation is provided in FIG. 8. In compensation therefor, a signalspecifying the pilot signal measurement time length and the innerthreshold value multiplexed onto the transmission signal from atransmission base station is separated in the demultiplexer (DMUX) 405,and the reception quality monitor 406 is informed of the pilot signalmeasurement time length and the transmission base station designatingsection 409 is informed of the inner threshold value. The multiplexer(MUX) 410 multiplexes the base station designating signal from thetransmission base station designating section 409 onto input data togenerate an up-transmission signal. Since operations of other componentsare similar to those of the second embodiment, explanation thereof isomitted.

In FIG. 14, the base station according to the present embodiment isfurther provided with the speed estimate device 517 in the base stationshown in FIG. 5. The speed estimate device 517 inputs the transmissionelectric power control signal multiplexed onto the transmission signalfrom the mobile station separated in the demultiplexer (DMUX) 505 andestimates the movement speed of the mobile station based upon the changein the transmission electric power control signal. This estimation isperformed for each mobile station with which a link is set up. Thesignal representing the speed of a mobile station estimated by the speedestimate device 517 is outputted to the output terminal 506, and thebase station controller is informed of that signal.

Since other operations in the base station are similar to those of thefirst embodiment, they are omitted.

Since the configuration and operations of the base station controllerare similar to those of the second embodiment, their explanation isomitted.

Next, a fifth embodiment of the present invention is explained. Althoughthe pilot signal measurement time length and the inner threshold valueare decided in the base station controller corresponding to the movementspeed of the mobile station estimated in the mobile station in the casesof the second embodiment, in the fifth embodiment, the pilot signalmeasurement time length and the inner threshold value are decided in thebase station, and the corresponding mobile station is informed of them.

In the mobile station, the pilot signal measurement time length and theinner threshold value are altered based upon the information from thebase station.

FIG. 15 is a diagram showing the configuration of the base stationaccording to the present embodiment, the same reference numerals aredesignated for the corresponding parts to those in FIG. 5, andoverlapping explanation thereof is omitted. The mobile station accordingto the present embodiment is the same as that of the second embodimentof FIG. 8. The cellular system to which the present embodiment isapplied is the same as that of FIG. 3.

In FIG. 15, the base station according to the present embodiment isprovided with a control section 512 comprised of a pilot signalmeasurement time length specifying section 513 and an inner thresholdvalue specifying section 514 with which the base station controller ofFIG. 6 is not provided.

The base station separates a signal representing the movement speed ofthe mobile station multiplexed at predetermined time intervals onto thesignal transmitted from the mobile station in the demultiplexer (DMUX)505 and informs the pilot signal measurement time length specifyingsection 513 and the inner threshold value specifying section 514 of theestimated speed. The reception quality measurement time length of thepilot signal and the inner threshold value are decided corresponding tothe estimated speed in the pilot signal measurement time lengthspecifying section 513 and the inner threshold value specifying section514, and signals specifying the length and the value are multiplexedonto the transmission signal in the multiplexer (MUX) 509 and areprocessed in the spread circuit 510, the radio transmission section (Tx)511, and the transmission/reception shared device (DUP) 502 to betransmitted from the reception antenna 501 to the mobile station.Operations of other components are performed similarly to those of thebase station of FIG. 5.

In operations of the base station in the present embodiment, a signalrepresenting the speed of the mobile station from the base station maybe received at step 1001 of FIG. 10 that is the flow chart showing theoperations of the base station controller of the second embodiment, andbased upon this speed V the pilot signal measurement time length and theinner threshold value may be decided at steps 1003, 1007 so that themobile station is informed of them.

Although in the second embodiment, the mobile station receives the pilotsignal measurement time length and the inner threshold value decided inthe base station controller via the base station so as to alter thepilot signal measurement time length and the inner threshold value, itis only different therefrom in the present embodiment that the mobilestation directly receives the pilot signal measurement time length andthe inner threshold value decided in the base station. Thus, since themobile station in the present embodiment can be realized by the sameconfiguration as that of the mobile station of the second embodimentshown in FIG. 8, its explanation is omitted.

Next, a sixth embodiment is explained. Although the pilot signalmeasurement time length and the inner threshold value are decided in thebase station corresponding to the movement speed of the mobile stationestimated in the mobile station in the case of the fifth embodiment soas to inform the corresponding mobile station of them, in the sixthembodiment, a movement speed is estimated in the base station for eachmobile station, and corresponding to the estimated movement speed, thepilot signal measurement time length and the inner threshold value aredecided in the base station, and the corresponding mobile station isinformed of them.

In the mobile station, the pilot signal measurement time length and theinner threshold value are altered based upon the information from thebase station.

FIG. 16 is a diagram showing the configuration of the base stationaccording to the present embodiment, the same reference numerals aredesignated for the corresponding parts to those in FIG. 15, andoverlapping explanation thereof is omitted. The mobile station accordingto the present embodiment is the same as that of the fourth embodimentof FIG. 13. The cellular system to which the present embodiment isapplied is the same as that of FIG. 3.

In FIG. 16, the base station according to the present embodiment isprovided with the speed estimate device 517 with which the base stationof FIG. 15 is not provided.

The speed estimate device 517 inputs the transmission electric powercontrol signal multiplexed onto the transmission signal from the mobilestation separated in the demultiplexer (DMUX) 505 and estimates themovement speed of the mobile station based upon the change in thetransmission electric power control signal. This estimation is performedfor each mobile station with which a link is set up. The pilot signalmeasurement time length specifying section 513 and the inner thresholdvalue specifying section 514 are informed of the signal representing thespeed of a mobile station estimated by the speed estimate device 517.Since other configuration and operations of the base station in thepresent embodiment are similar to those of the fifth embodiment, theirexplanation is omitted.

In operations of the base station in the present embodiment, the speedof the mobile station may be estimated at step 1001 of FIG. 10 that isthe flow chart showing the operations of the base station controller ofthe second embodiment, and based upon the estimated speed V the pilotsignal measurement time length and the inner threshold value may bedecided at steps 1003, 1007 so that the mobile station is informed ofthem.

Although in the fourth embodiment, the mobile station receives the pilotsignal measurement time length and the inner threshold value decided inthe base station controller via the base station so as to alter thepilot signal measurement time length and the inner threshold value, itis only different therefrom in the present embodiment that the mobilestation directly receives the pilot signal measurement time length andthe inner threshold value decided in the base station. Thus, since themobile station in the present embodiment can be realized by the sameconfiguration as that of the mobile station of the fourth embodimentshown in FIG. 13, its explanation is omitted.

The present invention is not limited to each embodiment described above.

For example, the base station controller in the present invention is notlimited to the configuration of FIG. 3 and may be individually installedin each base station.

Although one standard speed is set and the pilot signal measurement timelength and the inner threshold value are specified at two steps inrelation to the standard speed, a plurality of standard speeds may beset, and several steps of values may be set corresponding to the speedsso as to perform further detail alteration.

Although the embodiments are explained employing the movement speed ofthe mobile station as an example of a propagation environment or achange in a propagation environment, as another example for apropagation environment or a change in a propagation environment, thenumber of effective multipass can be deemed. Since the smaller thenumber of effective multipass the more macro-diversity effect isincreased, control may be performed so that the inner threshold value ismade greater.

INDUSTRIAL APPLICABILITY

As explained above, with the present invention, transmission basestations can be decided for each mobile station under an optimumcondition corresponding to the movement speed of the mobile station.Thus, transmission base stations can be decided so that the number oftransmission base stations can be decreased as small as possible and theprobability that the best base station is included in the transmissionbase stations is made higher. As a result, interference in downlink canbe decreased, and the link capacity can be increased.

1. A mobile communication control method in which one or a plurality ofbase stations transmit a pilot signal at a predetermined electric power,the method comprising: periodically measuring, by one or a plurality ofmobile stations, a reception quality of each pilot signal transmittedfrom the one or a plurality of base stations to decide one or aplurality of base stations with which links are set up corresponding tothe measurement result and decide one or a plurality of transmissionbase stations from among the decided one or a plurality of basestations, estimating, by the one or plurality of mobile stations, amovement speed of the mobile station, deciding, by the one or pluralityof mobile stations, a threshold value of the pilot signal quality basedupon the movement speed of the mobile station, and deciding, by the oneor plurality of mobile stations, the one or plurality of transmissionbase stations based upon the threshold value, wherein the faster themovement speed of the mobile station, the greater the threshold value ismade.
 2. A mobile communication control method in which one or aplurality of base stations transmit a pilot signal at a predeterminedelectric, power, the method comprising: periodically measuring, by oneor a plurality of mobile stations, a receptjon quality of each pilotsignal transmitted from the one or a plurality of base stations todecide one or a plurality of base stations with which links are set upcorresponding to the measurement result and decide one or a plurality oftransmission base stations from among the decided one or a plurality ofbase stations, estimating, by the one or plurality of base stations, themovement speed of the one or plurality of mobile stations, deciding, bythe one or plurality of base stations, a threshold value of the pilotsignal quality for each of the mobile stations based upon the movementspeed of the mobile station, and informing a corresponding mobilestation, and deciding, by the one or plurality of mobile stations, theone or plurality of transmission base stations based upon the thresholdvalue, wherein the faster the movement speed of the mobile station, thegreater the threshold value is made.
 3. A cellular system comprising:one or a plurality of base stations which transmit a pilot signal at apredetermined electric power, and one or a plurality of mobile stationswhich periodically measure a reception quality of each pilot signaltransmitted from the one or a plurality of base stations to decide oneor a plurality of base stations with which links are set upcorresponding to the measurement result and decide one or a plurality oftransmission base stations from among the decided one or a plurality ofbase stations, the one or a plurality of mobile stations estimatemovement speed of the mobile station, and decide a threshold value ofthe pilot signal quality based upon the movement speed of the mobilestation, and end of the mobile stations decides the one or plurality oftransmission base stations based upon the threshold value, wherein thefaster the movement speed of the mobile station, the greater thethreshold value is made.
 4. The cellular system according to claim 3,wherein the movement speed of the mobile station is estimated by themobile station.
 5. The cellular system according to claim 4, wherein themobile station includes means for multiplexing data corresponding to themovement speed of the mobile station, with transmission data to betransmitted to the base station.
 6. The cellular system according toclaim 5, wherein the base station includes means for demultiplexing thedata corresponding to the movement speed of the mobile station, from thetransmission data transmitted to the base station by the mobile station.7. The cellular system according to claim 3, wherein the movement speedof the mobile station is estimated by the base station.
 8. A cellularsystem comprising: one or a plurality of base stations which transmit apilot signal at a predetermined electric power, and one or a pluralityof mobile stations which periodically measure a reception quality ofeach pilot signal transmitted from the one or a plurality of basestations to decide one or a plurality of base stations with which linksare set up corresponding to the measurement result and decide one or aplurality of transmission base stations from among the decided one or aplurality of base stations, the one or plurality of base stationsestimates the movement speed of the one or a plurality of mobilestations, decides a threshold value of the pilot signal quality for eachof the mobile stations based upon the movement speed of the mobilestation, and informs a corresponding mobile station, and each of the oneor plurality of mobile stations decides the one or plurality oftransmission base stations based upon the threshold value, wherein thefaster the movement speed of the mobile station, the greater thethreshold value is made.
 9. A mobile station, comprising: means forreceiving a pilot signal transmitted from one or a plurality of basestations at a predetermined electric power; means for periodicallymeasuring a reception quality of each pilot signal transmitted from theone or plurality of base stations to decide one or plurality of basestations with which links are set up corresponding to the measurementresult, and deciding one or a plurality of transmission base stations;means for estimating movement speed of the mobile station; means fordeciding a threshold value of the pilot signal quality based upon themovement speed of the mobile station; and means for deciding the one ora plurality of transmission base stations based upon the thresholdvalue, wherein the faster the movement speed of the mobile station, thegreater the threshold value is made.
 10. The mobile station according toclaim 9, further comprising: means for multiplexing data correspondingto the movement speed of the mobile station, with transmission data tobe transmitted to the base station.
 11. A base station, comprising:means for transmitting a pilot signal at a predetermined electric power,means for deciding one or a plurality of base stations with which linksare set up decided corresponding to a reception quality of the pilotsignal periodically measured in one or a plurality of mobile stations,and receiving information of one or a plurality of transmission basestations selected from among the decided one or a plurality of basestations, means for estimating the movement speed of the one or aplurality of mobile stations, means for deciding a threshold value ofthe pilot signal quality for each of the mobile stations based upon themovement speed of the mobile station to inform a corresponding mobilestation, and means for letting the one or a plurality of mobile stationsdecide the one or plurality of transmission base stations based upon thethreshold values, wherein the faster the movement speed of the mobilestation, the greater the threshold value is made.
 12. The base stationaccording to claim 11, further comprising: means for demultiplexing datacorresponding to the movement speed of the mobile station, fromtransmission data transmitted to the base station by the mobile station.